Background: Antibiotic resistance mediated by extended spectrum beta lactamase (ESBL) and AmpC enzymes in Escherichia coli continue to be a major threat in a health care setting. This study was undertaken to calculate the prevalence and to characterize ESBL and AmpC enzymes produced by E. coli by various phenotypic and molecular methods (polymerase chain reaction [PCR]).
Materials and Methods: A total of 196 clinical isolates of E. coli were screened for ESBL production using cephalosporin disk diffusion method, minimum inhibitory concentration (MIC) determination by E-test and Vitek-2 system. Phenotypic confirmation for ESBL production was done using cephalosporin/clavulanate combination disc test method and E-test for ESBLs. For the detection of AmpC enzymes, cefoxitin disk diffusion and cefoxitin MIC testing was used and further phenotypically confirmed by three dimensional extract test, AmpC disk test, boronic acid disk test method and disk approximation method. The genotypic detection of ESBL genes and AmpC genes were done by PCR.
Statistical Analysis: The data was analyzed using SPSS software (Version 21.0). Chi-square test was used for statistical analysis of the data.
Results: The prevalence of ESBL and AmpC enzymes among E. coli isolates was found 93.12% and 28.68%. Among the various phenotypic screening methods evaluated, ceftazidime (CZD) disk diffusion test had the highest sensitivity of 90.67% and positive predict value of 92.86% followed by cefotaxime and CZD in comparison with polymerase chain reaction (PCR). For AmpC β-lactamases, the cefoxitin disk used for screening of AmpC β-lactamases had sensitivity of 91.67%, specificity of 59.14%, positive predict value of 46.48%, and negative predict value of 94.83% when compared with PCR.
Conclusion: The high prevalence of ESBL and AmpC in our study emphasises on the judicious use of antibiotics in controlling antimicrobial resistance in the hospital.